A multispectral imaging approach integrated into the study of Late Antique textiles from Egypt

Abstract

This work explores the use of multispectral imaging (MSI) techniques applied to the investigation of Late Antique (c. 250–800 AD) textiles found in Egypt. Although the use of these techniques is well-established in the study of polychrome surfaces, they have only been sparingly and often unsystematically applied to the investigation of textiles. The aim of this work is therefore to bridge this gap by showing how this non-invasive, relatively inexpensive and portable methodology can be used to map the photoluminescence and reflective characteristics of textiles under different wavelengths of light, and to provide qualitative and holistic insights into the chemical nature of the materials that compose them. Standardised acquisition and post-processing methods were applied to produce visible-reflected (VIS), ultraviolet-induced visible luminescence (UVL), infrared-reflected (IRR), infrared-reflected false colour (IRRFC), ultraviolet-reflected (UVR) and ultraviolet-reflected false colour (UVRFC) images that provided preliminary indications of the colourants used and their spatial distribution. This proved to be an important aid in planning more targeted and effective sampling strategies and facilitated comparisons between objects. Visible-induced visible luminescence (VIVL) and multiband-reflected (MBR) imaging were also explored for the first time with application to textiles, demonstrating their potential in mapping red and blue colourants respectively. The physical properties observed from all of these images were then related to the more detailed information provided by complementary non-invasive techniques, such as fibre optic reflectance spectroscopy (FORS), and micro-invasive approaches, such as high-performance liquid chromatography mass spectrometry (HPLC-MS). Guidelines towards the interpretation of complex MSI images and a discussion of the potential and limitations of relating multispectral data to chemical properties are presented. An important result of this work is the delineation of a protocol, which combines optical microscopy (OM), MSI, FORS and HPLC-MS and shows a high degree of potential, not only for the investigation of Late Antique textiles but for textiles in museum and historic collections generally.

In search of Humboldt’s colors: materials and techniques of a 17th-century lacquered gourd from Colombia

“…In accordance with his description, IRRFC and UVRFC images of the gourd's green background suggested the presence of indigotin, which showed as red in the former, and of organic yellows, which showed as red in the latter (Fig. 7) [78][79][80]. The use of indigotin was conclusively confirmed by FORS ( Fig.…”

“…The organic nature of these colorants was further supported by UVRFC imaging of the object (Fig. 7a), in which all yellow dyes typically show as red [78][79][80]. From an analytical standpoint, FORS is generally not suitable to characterize yellow colorants, as their spectra appear broad and featureless, while SERS, again, yielded no results due to the hard texture of the embedding resin, thus interfering with the analysis.…”

Exploring the transition from natural to synthetic dyes in the production of 19th-century Central Asian ikat textiles

“…Non-destructive surface techniques, such as UV-Vis reflectance and luminescence spectroscopies, have been applied to identify a limited number of colorants [45][46][47][48][49][50][51]. Similarly, multispectral imaging (MSI) has been recently introduced as a useful tool for studying the distribution of the dyes on large surfaces with the possibility to identify selected dyes [52][53][54][55]. Nonetheless, non-invasive investigations produce limited information, especially when it comes to yellow dyes, most of which are hardly distinguishable from each other in terms of their fluorescence and reflectance spectra, or dye mixtures.…”

“…Nonetheless, non-invasive investigations produce limited information, especially when it comes to yellow dyes, most of which are hardly distinguishable from each other in terms of their fluorescence and reflectance spectra, or dye mixtures. As a result, recent studies have focused on the delineation of protocols aimed at identifying dyes in textiles using a combination of non-invasive techniques (microscopy, FORS and MSI), whose results can guide a selective sampling of areas of particular interest to be analyzed by HPLC techniques [40,54,[56][57][58].…”

Compositional and Micro-Morphological Characterisation of Red Colourants in Archaeological Textiles from Pharaonic Egypt

“…The chemical analysis of richly coloured Egyptian textiles from the first millennium CE has a long-standing tradition [14,15,16,17], whereas less attention has been given to the systematic investigation of the dyes used in Pharaonic textiles from the first millennium BCE with state-of-the-art scientific techniques. The published studies [1,4,18,19,20] indicate that sources of red colourants used to dye textiles were mainly ochreous earths and plant dyes.…”